At least some known gas turbine assemblies are used for electrical power generation. Such gas turbine assemblies include a compressor, a combustor, and a turbine. Gas (e.g., ambient air) flows through the compressor, where the gas is compressed before delivery to one or more combustors. In each combustor, the compressed air is combined with fuel and ignited to generate combustion gases. The combustion gases are channeled from each combustor to and through the turbine, thereby driving the turbine, which, in turn, powers an electrical generator coupled to the turbine. The turbine may also drive the compressor by means of a common shaft or rotor.
In some combustors, the generation of combustion gases occurs at two, axially spaced stages. Such combustors are referred to herein as including an “axial fuel staging” (AFS) system, which delivers fuel and an oxidant to one or more fuel injectors downstream of the head end of the combustor. In a combustor with an AFS system, a primary fuel nozzle at an upstream end of the combustor injects fuel and air (or a fuel/air mixture) in an axial direction into a primary combustion zone, and an AFS fuel injector located at a position downstream of the primary fuel nozzle injects fuel and air (or a second fuel/air mixture) as a cross-flow into a secondary combustion zone downstream of the primary combustion zone. The cross-flow is generally transverse to the flow of combustion products from the primary combustion zone.
In some cases, it is desirable to introduce the fuel and air into the secondary combustion zone as a mixture. Therefore, the mixing capability of the AFS injector influences the overall operating efficiency and/or emissions of the gas turbine.
Moreover, in some instances, the type of fuel introduced by the AFS injector has been limited to fuels having a heat release or a Modified Wobbe Index value in a prescribed range, in order to maintain emissions-compliant operation. Therefore, an AFS injector capable of introducing fuels having a wide range of heat release values without generating unacceptable levels of emissions is also desirable.